May, 1910.1 



409 



Plant Sanitation! 



refers to Wright's advice re the use 

 of Bordeaux mixture against canker. 

 Wright's advice, however, was based on 

 a misapprehension of the nature of the 

 diseases he was treating; he adhered 

 firmly to the belief that the pod and 

 stem diseases were identical, and there- 

 fore imagines that in spraying the pods 

 he was combating the stem disease. 

 As the two diseases are different, his 

 results with Bordeaux mixture are not 

 relevant to canker. However, the re- 

 sults quoted by von Faber, viz., a 

 diminution in the number of cankered 

 trees from 96 per cent, in 1902 to 4*3 

 per cent, in 1904 were obtained before 

 the estate was sprayed. They can only 

 be attributed, therefore, to removal of 

 shade and excision of diseased tissues. 

 Similarly, the results of the work against 

 pod disease from 1902 to 1904, illustrated 

 by Wright's diagrams, are to be attri- 

 buted to the removal of shade and the 

 regular collection ot diseased pods, not 

 to spraying. 



The section dealing with Diplodia 

 illustrates the confusion which has 

 arisen through the transmission of 

 disease specimens to Europe. Nine pages 

 are devoted to the discussion of the 

 several species which have been found 

 on cacao. But recent researches have 

 shown that these are all the same 

 species, and that, in general, it is only 

 saprophytic ! When twigs have been 

 killed by exposure to the sun, or by 

 Helopeltis, Diplodia may act as a wound 

 parasite, and, after growing on the 

 dead twig, may attack the still living 

 part of the branch and kill it further 

 back, but only in this case is it known 

 to cause damage. 



It is interesting to note that the 

 damage which is attributed to squirrels 

 in Ceylon is attributed to rats in other 

 countries. In the West Indies it has 

 been claimed that spraying the stem 

 with Bordeaux mixture keeps away rats, 

 but it is difficult to understand how 

 this could be effective if the branches 

 of adjacent cacao trees touched one 

 another as they usually do. 



One is rather surprised to find in 

 the third chapter an account of a Pera- 

 deniya experiment which proves the 

 advantage of a wind-belt. It is pub- 

 lished on page 66 of Wright's book. 

 The result is as follows, the numbers 

 being the number of fruits per acre. 



Without With 

 wind-belt, wind-belt. 



1903 ... 1,275 2,463 



1904 ... 2,942 5,268 



1905 ... <l,023 6,430 



The experiment was proposed in 1903, 

 and the wind-belts were to be planted in 

 52 



October of that year. The figures for 

 1903, therefore, merely give the original 

 condition of the plots. The average 

 number of fruits per acre for the whole 

 estate was, in 1,903, 2,322 ; in 1904, 3,796 ; 

 and in 1905, 7,117. The plot without a 

 wind-belt was therefore much below the 

 average, and it would have been better 

 if two more equal plots had been 

 chosen. It may be noted that the wind- 

 belt plot drops below the average in 

 1905. From the report for 1903, it 

 appears that eight wind-belt experi- 

 ments were planned. The trees selected 

 for the different belts were Grevillea 

 robusta, Michelia champaca, Pterocarpus 

 echinatus, Eugenia jambos, arecanuts, 

 Filicium decipiens, Castilloa, and Ery- 

 thrina iithosperma. Each was to be 

 planted in the form of a square, 40 

 yards by 40 yards, and all shade trees 

 and palms within 75 yards of a square 

 were to be removed. The 1904 report 

 gives no further information, except 

 that it is stated that the number of 

 Michelia on the estate is due to the 

 newly-planted wind-belts ; and there is 

 nothing about them in the report for 



1905. There are no records which would 

 inform us which of these wind-belts 

 provided the figures quoted, or where 

 they were situated. It is probably a 

 mere coincidence that 2,463 is the crop of 

 plot 33 in 1903, and 5,268 is the crop of 

 the same plot in 1904, since its crop for 

 1905 is not 6,430, but 8,088. The control 

 plot selected in 1903 was No. 44 (5 acres) ; 

 it was to be cleared of everything except 

 cacao, and the 1903 report states that 

 " already it has become a congested 

 centre of troublesome weeds." Appa- 

 rently it was not subsequently kept as a 

 control plot, for in July, 1904, it bore, in 

 addition to the cacao, 93 coconut and 

 areca palms, and 74 other trees, and in 

 July, 1905, 85 coconuts and areca, 1,577 

 dadaps, and 40 other trees. Its crop 

 for the three years under discussion was 

 12,758, 18,480, and 36,471 pods. 



The experiment is not included in a 

 list of experiments in progress furnished 

 to the Committee at the beginning of 



1906. Apparently it was abandoned at 

 the end of 1905 and the trees removed ; 

 consequently it is not possible to furnish 

 figures for other years, nor to say 

 where the plots were. But it is obvious 

 that trees planted in October, 1903, could 

 not have afforded an efficient wind-belt 

 for old cacao in either 1904 or 1905 ; hence 

 whatever may be the value of the figures 

 they do not represent the advantage of 

 a wind-belt. 



It may further be noted that on the 

 plot with the wind-belt the increase in 

 1904 is 114 per cent., and in 1905, 22 per 



